Override some theme's css

It seems, Code of Conduct again successfully works!  But
code review - doesn't.  They introduce readthedocs/sphinx_rtd_theme#329 again.

Workaround readthedocs/sphinx_rtd_theme#687

docs/_static/custom.css

@@ -0,0 +1,3 @@
+.rst-content div[class^="highlight"] pre {
+    line-height: normal;
+}

docs/conf.py

@@ -106,3 +106,12 @@
 # This value controls if docstring for classes or methods, if not explicitly
 # set, is inherited form parents.
 autodoc_inherit_docstrings = False
+
+# A list of paths that contain custom static files. Relative paths are taken as
+# relative to the configuration directory. They are copied to the output’s
+# _static directory.
+html_static_path = ['_static']
+
+# https://docs.readthedocs.io/en/latest/guides/adding-custom-css.html
+def setup(app):
+    app.add_stylesheet('custom.css')